Loudspeakers are fundamental components of an audio system. Loudspeakers are electroacoustic transducers that produce sound in response to receiving an electrical audio signal input. Generally, loudspeakers include a diaphragm and an electromechanical driver unit. The electromechanical driver unit receives the electrical audio signal input and produces physical movement in response to the electrical audio signal input. The electromechanical driver unit may be physically connected to the diaphragm such that the physical movement of the electromechanical driver unit drives movement in the diaphragm which moves air causing a pressure wave that transmits sound to a user's ears.
For most sound system applications, the goal is to produce loudspeakers that reproduce recorded or amplified input sounds with some type of acceptable fidelity to the original recorded or input sound. The problem in producing these loudspeakers is that there are numerous ways to design them technically with varying levels of performance, cost, and complexity. Generally, the designs need to be tested to evaluate their respective performance.
Input based approaches may be used to test loudspeakers. A given input signal may be introduced into the loudspeaker and the corresponding output is then measured. As an example, if a 50 watt input electrical audio signal is introduced into a given loudspeaker, the output sound correspondingly produced by the loudspeaker is measured for such things as frequency response, directivity, sound intensity (i.e., loudness), fidelity, etc. If different loudspeakers are tested relative to each other, the same approach is used in that each loudspeaker receives the same input reference signal and the corresponding output of each loudspeaker is measured and compared. It is basically a filter test where inputs are known, the outputs are measured, and the transfer functions of the filters are compared. Unfortunately, different loudspeakers do not react uniformly to the same input stimulus. Specifically, loudspeakers may react very differently based on the same input stimulus. For example, one loudspeaker may produce a sound level that is very much louder than another loudspeaker for the same given input power. Similarly, one loudspeaker may produce much higher fidelity sound for a given type of input signal than another loudspeaker. Due to the differing reactions of loudspeakers, it is difficult to design proper testing procedures for testing different types of loudspeakers.